Over the years, when the subject of religion comes up in some
connection, students in my classes seem to make very decided
distinctions between "religious" and "spiritual." But each of them seems
to have made up a somewhat different version of the distinction....

I have a very decided distinction between those two words. To me,
"religious" connotes "institutional," while "spiritual" does not. I.e.,
you are religious if you go to church, observe the practices of your
religion, etc. You may be spiritual and not religious -- certainly you can
be religious and not at all spiritual.